This invention relates generally to improvements in a hydraulic pressure regulating system, and more particularly to a device for regulating a hydraulic pressure in a transmission control system for such a vehicle of the type being provided with a fluid actuated frictionally engaging means, such as a clutch or brake means.
It is required in the operation of a vehicle that the frictional engagement of a clutch or brake device be smooth with as small of an impact as possible. Upon a conventional transmission being fluidically shifted to a forward or a rearward drive position, such shifting often results in the frictionally engaging means being abruptly engaged thereby to bring about a great impact and, in consequence, not only to give a feeling of discomfort to the occupants of the vehicle but to cause damages to various parts thereof.
To obviate this deficiency, there has been introduced in such vehicles a fluid pressure control means such as an orifice and an accumulator or modulator valve in a conduit between a regulator valve regulating the pressure of the fluid discharged from an oil pump to be sufficient for fluid actuated means, such as a clutch means, in a maximumly loaded driving condition of the vehicle and such fluid actuated means. According to the conventional method above-mentioned, however, the fluid under pressure regulated by the regulator valve is rather high in comparison with the fluid pressure needed for the full engagement of the fluid actuated means during an ordinary running condition, so that there still remains an impact in the engaging operation of such fluid actuated means. Otherwise the fluid pressure control valve will be much more complex in construction, bigger in size and more expensive in manufacturing cost. These deficiencies are considered to be greatly disadvantageous in practice.